The present invention relates to a method and device for determining the state of a rechargeable battery.
Complex impedance analysis is performed to determine the state of a battery. This technique allows the battery state to be determined without destroying the battery. Thus, the battery can be reused when determined that the battery is normal.
International Patent Publication No. WO2013/115038 discloses one example of a determination device that determines the state of a rechargeable battery based on the complex impedance analysis.
The determination device described in International Patent Publication No. WO 2013/115038 applies AC voltage to a rechargeable battery while varying the frequency in steps. Further, the determination device obtains the gradient of two or more impedances measured at different frequencies in a diffusion region of the rechargeable battery. Then, the determination device compares the inclination angle with a threshold value. When the inclination angle is greater than or equal to the threshold value, the determination device determines that the capacity balance of the battery is normal. When the inclination angle is less than the threshold value, the determination device determines that the capacity balance of the battery is abnormal. Further, when the level of an imaginary axis of the complex impedance in the diffusion region of the rechargeable battery is greater than a threshold value, the determination device determines that the capacity balance of the battery is abnormal. When the level of the imaginary axis of the complex impedance is less than or equal to the threshold value, the determination device determines that the capacity balance of the battery is normal.